Equatorial precision sundial



y 9, 1940. J. P. M. GUADET 2,207,195

EQUATORIAL PRECIS ION SUNDIAL Filed May 25, 1958 2 Sheets-Sheet l y 9, 1940. J. PIM. GUADET- 2,207,195

EQUATORIAL PRECISION SUNDIAL F'iled May 25, 1938 2 Sheets-Sheet 2 F IG. 2 26 Patented July 9, 1940 UNITED STATES PATENT orri ce Application May 25, 1938, Serial No. 210,077 In France June 4, 1937 5 Claims.

Application was filed in France on June 4, 1937 and in Germany on February 7, 1938.

This invention relates to an equatorial precision sundial and one object of the invention is to provide a sundial which can be regulated in various ways so that, wherever operated, the plane of the dial can be disposed in a plane parallel to the equatorial line and thus make it possible, byrotating the dial in its own plane, to place it in the correct position for accurately indicating local time either at the place from which mean time is computed or at a distance therefrom.

Another object of the invention is to provide a sundial including a device permitting reading of the time on the dial by means of a luminous ray passing through a slot between two opaque prisms, the prisms being so mounted that their sharpest edges, placed opposite each other, are parallel and at a slight distance from each other.

Another object of the invention is to so mount the prisms, which are preferably cast in one piece, that they can rotate about an axis which coincides with the slot, the prisms being surmounted by a convex mirror having its reflecting surface lowermost in order to permit use of the sundial in autumn, winter, spring and summer.

Another object of the invention is to provide a sundial which is simple in construction, easy to adjust when set up for use, and of strong construction so that it will not be liable to get out of order.

The invention is illustrated in the accompanying drawings wherein:

Fig. 1 is a perspective view of the improved Fig. 2 is a view showing the sundial partially in section and partially in elevation.

Fig. 3 is a plan view of the prisms and the disk carrying the same, the convex mirror being removed.

Fig. 4 is a view similar to Figure 2 convex mirror in place.

Fig. 5 is a view of the dial looking at the having graduations thereon.

Figs. 6, '7 and 8 are diagrammatic views illustrating the operation of the improved sundial.

As seen from the drawings, the sundial is mounted on a T-shaped base i and provided with adjusting screws 3' which serve as a three-point support and permit angular adjustments to be made relative to a horizontal plane. The T- shaped base is surmounted by a frame 2 having the shape of an inverted Y and the feet 3 of the frame are secured by certain of the screws 3' showing the face which pass through aligned threaded openings formed in the feet of the frame and companion portions of the base. This frame is supported at an incline by a brace 5 formed by two sections which slidably engage eachother and are held in adjusted positions by the screw 6. The upper end of the brace engages a cleat carried by-the arm 8 of the frame 2 as indicated by the dotted lines in Figure l and the lower section of the brace is provided with a foot I through which the rear screw 3' passes.

At the center of the rear face of the dial N there is a cylindrical boss 9 formed withan opening or bore Iii, this boss serving as a pivot for the dial and being engaged through an opening formed in the support 2 so that the plane of the dial is parallel to that of the inclined supporting frame and may be rotated onits axis. The usual hour-markings are provided upon the front face of the dial as shown at E2, and the upper portion of its periphery bears a corrective scale as shown at I3, the use of which will be set forth hereinafter. g

The opening or bore ill of the pivot 9 receives the pin M of a small circular plate [5 carrying the two prisms l6 and H. are of elongated triangular formation when viewed in end elevation with a rectangular part leading from the base of the triangle and their sharpedges from each other, as shown in Figure 3, to provide an opening or slit l8 through which sunlight may pass and throw a luminous ray on thetime graduation scale I2.

In order to prevent the base of the prismcarrying plate l5 from wearing the surface of the These two prisms dial, which is preferably enamelled a wear-absorbing plate is interposed between the upper or front face of the dial l l and the rear or lower face of the plate [5. This wear-absorbing plate i5 is viixedto ,the'face of the dial H and very effectively prevents the plate l5 from rubbing against the enamelled surface of the dial when turning.

The upper or outerend of one-prism carries a strip 25 having a V-shaped notch IS in its inner endand the other prism carries a strip 26 having a straight-cut inner end so that a concave convexed mirror 2| may be mounted against these strips and rest on three points. The concaved face of the mirror is protected by a pad 22 of rubber or cork, so as to prevent it from being worn by the end of a thrust screw 23 threaded through a clip or yoke 24 supported in its turn by the outer ends of the strips 25 and 2B which project outwardly from the upper ends of the prisms l6 and I1. This thrust screw maintains the mirror rigidly against the inner ends of the strips l9 and 20 and firmly but detachably holds it in place. The whole assembly, prisms and mirrors, can rotate with the pin M which can not slip out of the opening Ill, being maintained therein by the washer and nut 2'! applied to the threaded end portion of the pin.

To regulate the sundial, the brace is adjusted to a suitable length, according to the indications of a numerical table, and the latitude of the place of operation, so that the dihedral angle of the plane of the dial and the plane of the base [will be equal to the dihedral of the plane of the equator and of the horizontal plane of the place of operation. The base is placed on an approximately horizontal plane in such a position that a line extending longitudinally of the cross head of the base runs east and west, the screws 3' being then adjusted to level the base. If the correct time is known, the best method is to regulate the orientation last, after all other regulations have been effected, even those indicated later for the position of the dial in its plane; the apparatus being merely rotated on the horizontal plane of the support so as to give the exact time.

If the correct time is unknown, the operator will resort to a method similar to the classical system of the shadow length, utilizing the mark or pointer 29 shown at the top of the arm 8 of the frame 2 in Figure l. The plane of the disk can be adjusted parallel to that of the equator by either method, knowledge of time or by the system indicated. It is clear that the foot must be adjusted horizontally according to the usual practice.

The apparatus thus adjusted, the luminous ray passing through the slot l8 turns equal angles in equal time, so that the apparatus gives the correct time throughout the day, after it has once been regulated to indicate the exact time at a given moment.

The position of the dial in its ownplane is determined by the following principle:

The apparatus being suitably adjusted, the luminous ray passing through the slot l8 falls according to the line of the greatest inclination of the dial at the moment when the sun passes through the meridian of the place of operation. According to this line of greatest inclination should be found the division of the graduation 12 corresponding to the local time at that moment. The corrective graduation l3 is established from 0 to 600, the sign 0 being diametrically opposite 103428 of the general graduation, and the sign 600 being diametrically opposite 1434'28". In these conditions, to make the necessary adjustment, all that is necessary to place opposite guide 29, on the line of the greatest inclination from the centre of the dial, the division of graduation [3 obtained by the formula:

The first is an arbitrary number which is used so that the result of the addition shall not be negative. The number 23 will be'employed if the longitudes used for calculating the term N are based on the Greenwich meridian and not used if the longitudes are based on the Paris meridian. The term N represents the longitude expressed in grades and multiplied by 9 or again expressed in degrees and multiplied by 10. This term N should be added if a west longitude is concerned and subtracted in the case of an east longitude. Term T depends daily on the difference between sun and mean midday time and is obtained from a numerical table for each day of the year (from 0 for November 3 to 77 on February 11). An additional term should be added to the formula if it is desired to ascertain the time according to a system other than that of France. The second 150 should be used only in summer time.

After adding together all the terms of the formula, we obtain a number, perhaps 200. The dial is then turned on its axis so as to bring 200 of the graduation i3 opposite the fixed pointer 29 which is on the vertical arm 8 of the frame 2. The dial is then finally adjusted.

It should be noted that the first number 150 is only correct for countries of the time system 0 (France, Great Britain, etc.) for the time system 1 (Germany, etc.) it must be replaced by 300. For time system 2 (Finland, etc.) it must be replaced by 450 and so on.

For time system 23 (Iceland, Maderia, etc.) Formula 1 should be maintained and 150 deducted from the result, 300 for time system 22 and so on. Finally certain States have a legal time which is independent of the various time systems. Thus, for Holland, 49 should be added to the normal formula (1), for Persia 515.

An apparatus with the dial as designed (Fig. 5) and with calculations made as indicated, can only be used in the Northern Hemisphere, but it is possible to construct similar apparatus for the Southern Hemisphere with simple modifications and embodying the main principles.

According to the time of day and the precision desired, the prism and mirror series can be adjusted at will and the luminous ray will be more or less wide.

The convex mirror surmounting the prisms and which can be easily removed is unnecessary during the period when the sun on the front or upper side of the dial as regards the equator plane, i. e. on the side of theNorthern Hemisphere, from the spring equinox to the autumn equinox. On the contrary, from the autumn equinox to the spring equinox, when the direct light of the sun falls only on the obverse or underside of the dial, it is necessary to use the convex mirror. The mirror is lighted by the sun, and reflects the light, directing it through the slot.

The invention also includes a device by which, instead of the two prisms (oifering the advantage of perfect rigidity), an indicator can be afiixed perpendicular to the plane of the dial. What has been said above for the luminous ray passing through the slot also applies to the shadow of the indicator and the mirror can be fixed to the end of the indicator by a system of claws.

The invention can be satisfactorily carried out with the following dimensions:

25 centimeters for the diameter of the main dial.

5 centimeters for the diameter of the prism bearing plate.

5 centimeters for the heightof the prisms.

5 centimeters for the diameter of the mirror.

5 centimeters for its focal distance.

I therefore claim:

1.,A sundial comprising a base, an upright frame carried by said base, a prop for supporting said frame at an incline and extensible to regulate the incline of the frame, fasteners for securing the frame and prop to said base constituting means for leveling the base, a dial'pivoted on and against the front face of said frame and having a circumferentially extendinghourscale upon its front face, the front face of the dial also bearing an arcuate correction scale adjacent the upper portion of its periphery said frame ex- 1 tending above the dial and having an indicator in cooperating relation to the correction scale, a carrier located centrally of said dial and projecting from the front face thereof concentric to the hour scale and the correction scale, and prisms projecting forwardly from said carrier, said prisms extending radially of the carrier in alinement with each other and being substantially triangular with their feathered edges disposed inwardly and terminating in slight spaced relation to each other to provide a narrow slit between theprisms at the center of the carrier for defining a pencil of light rays radially across the dial and the hour scale.

2. A Sundial comprising a base, an upright frame carried by said base and having downwardly diverging legs and an upwardly extending arm, an extensible prop back of said frame having its upper end engaging said arm and its lower end resting upon said base, said prop supporting said frame at a predetermined rearward incline, a dial pivoted on and against the front of said frame bearing upon its front face a circumferentially extending hour-scale, said dial carrying adjacent the upper portion of its periphery an arcuate correction scale, said dial being mounted for rotary adjustment, the upper end portion of the arm of said frame being projected upwardly above the dial and bearing an indicator in cooperating relation to the corrective-scale, and means extending forwardly from the dial centrally thereof for defining a pencil of light rays upon the front face of the dial radially of the dial and across the hour-scale in cooperating relation thereto.

3. A sundial comprising a frame, means to support said frame at a rearward incline, a dial in front of said frame bearing upon its front face a circumferentially extending hour-scale, a disk covering the central portion of the front face of said dial, a stem for said disk extending through said dial centrally thereof, prisms symmetrically carried by said disk and projecting forwardly therefrom, said prisms extending radially of the dial in opposed relation to each other and being tapered towards their inner side edges, the said inner side edges being spaced from each other a slight distance to provide a narrow slit for defining a pencil of light rays across the dial radially thereof in cooperating relation to the hour-scale.

4. A sundial comprising a frame, means to support said frame at a rearward incline, a dial in front of said frame bearing upon its front face a circumferentially extending hour-scale, prisms symmetrically carried by said dial and projecting forwardly from the central portion of said dial and extending radially of the dial in opposed relation to each other at opposite sides of the center of the dial, said prismsbeing tapered towards their inner side edges and having their inner side edges spaced from each other to provide a narrow slit aligned with the center of the dial for defining a pencil of light rays across the front face of the dial radially thereof in cooper ating relation to the hour-scale, and a convexed mirror mounted in confronting relation to outer ends of said prisms and having its center aligned with the center of the dial and the slit between the inner side edges of the prisms.

5. The structure of claim 4 wherein the prisms are provided with arms extending from outer ends of their outer side portions, a yoke disposed outwardly from said prisms and having its end portions engaged with said arms, said mirror being of concave-convex formation with its convex face presented towards the prisms and resting upon said arms, and a screw carried by said yoke and serving as means for releasably holding the mirror firmly in place.

JULIEN PAUL MARIE GUADET. 

